The present invention is directed to a method of monitoring cylinder wall wear of an internal combustion engine. The method involves the introduction of ultrasonic waves in the cylinder wall for detecting minute changes in the thickness of the cylinder wall resulting from wear.
Cylinder wall wear in an internal combustion engine occurs during the use of the engine due to the sliding contact of the piston and rings thereon against the adjacent cylinder wall. When the wear becomes excessive, the operating efficiency of the engine can be substantially reduced and/or cylinder wall failure can occur thereby rendering the engine inoperative. When the engine is rendered inoperative at an unexpected time, serious economic problems and possible human safety problems can arise, depending upon the application of the internal combustion engine. In large diesel engines in locomotives, for example, an entire train can be stranded on the tracks until emergency service is made available. Failure of the engine in an airplane can be catastrophic.
One attempt to avoid breakdowns due to engine cylinder wall failure is to periodically replace or overhaul the engine cylinder wall as by replacing a cylinder liner therein, after a fixed period of engine use, e.g., hours of engine operation, miles traveled, or other indicator. However, one problem associated with this proposed solution is that the fixed number of hours of operation or mileage before engine overhaul or replacement is an average figure, so that some engines will be overhauled or replaced prematurely while others may still fail before they are due for servicing or replacement. Instances of this last mentioned case increase the cost of operation of the motor driven device and are therefore undesirable.
An object of the present invention is to provide a method of monitoring cylinder wear which overcomes the aforementioned disadvantages associated with the operation and use of internal combustion engines. The method involves introducing ultrasonic waves in a cylinder wall of the engine, so that the waves travel through the cylinder wall.
It has been proposed in U.S. Pat. No. 4,123,943 to introduce ultrasonic waves in an engine cylinder so that the waves travel through the cylinder wall for the purpose of measuring cylinder wall thickness prior to machining the cylinder wall. This known method involves immersing the body in a coupling fluid, generating an ultrasonic signal within the cylinder bore and sensing signal reflections from the inner and outer wall surfaces. High frequency pulses are counted between the occurrence of a pulse and receipt of the first and second reflected pulses. The count is adjusted for differences in the velocity of sound in the different media to determine the thickness of the engine cylinder wall.
This known method is not suitable for use in an engine once it has been assembled and is operating in its intended environment because of the requirement for immersing the body in a coupling fluid. Moreover, this known method relates to the measurement of absolute thickness and the accuracy of the measurement is at best on the order of 0.01 mm.
U.S. Pat. No. 4,510,793 discloses a method of monitoring the wear of a refractory lining of a metallurgical furnace wall which involves the steps of arranging a bar of ceramic material in a hole drilled in the refractory lining, so that the bar has an inner end at the inner face of the lining and extends to the exterior of the wall. The bar is thus subjected to wear at its inner end as the lining wears. The position of the worn inner end of the bar is determined ultrasonically by generating ultrasonic pulses in the bar and detecting the reflecting of the pulses from the worn inner end of the bar. The conventional traveling time measurement technique is likewise employed for measuring the wear as the desired accuracy is only about 1 to 2 cm according to the patent.
A further object of the present invention is to provide a method of monitoring engine cylinder wall wear which avoids the aforementioned disadvantages with the prior art methods referred to such that the wear of the engine can be monitored continuously, if desired, throughout the life of the engine and with a high degree of accuracy so that thickness changes on the order of 0.0001 mm can be detected, and without necessitating drilling a hole through the cylinder wall or the use of special bar positioned within such a hole.
These and other objects are attained by the method of monitoring cylinder wall wear according to the present invention. As noted above, the method comprises the step of introducing ultrasonic waves in an engine cylinder wall, so that the waves travel through the cylinder wall. Further, the method includes the steps of determining a change in the traveling time of the ultrasonic waves traveling through the cylinder wall due to cylinder wall wear. The amount of wear of the cylinder wall is then calculated by multiplying the velocity of the ultrasonic waves in the cylinder wall by the traveling time change due to cylinder wall wear.
According to a disclosed preferred embodiment of the method, the change in the traveling time of the ultrasonic waves traveling through the cylinder wall due to cylinder wall wear is determined by using the phase comparison technique (For example, R.J. Blume, Rev. Sci. Instrum. 34, 1400 (1963); H. KWUN, J. Appl. Phys. 57, 1555 (1985)). The phase comparison technique enables small changes in traveling time of the waves on the order of 10.sup.-11 second to be determined. More specifically, the change in travel time due to wear is determined by measuring the resulting change in the phase of the travelling ultrasonic waves. As the velocity of ultrasonic waves in the cylinder wall depends on the temperature of the cylinder wall, the actual change in travel time must be adjusted to compensate for any change in travel time due to temperature variation of the cylinder wall to obtain travel time change due to wear. The temperature of the engine cylinder wall is monitored according to the method of the invention to enable compensation for travel time change due to temperature variation.
In the disclosed embodiment of the invention, the ultrasonic waves are introduced at or near an outer peripheral surface of a liner by means of an ultrasonic transducer. The ultrasonic waves transmitted by the transducer travel to the inner surface of the cylinder wall and are reflected back toward the outer peripheral surface thereof where they are detected by the same or a separate ultrasonic transducer. With the method of the invention, the wear of the liner of internal combustion engine can be monitored continuously during operation of the engine.